Glycosylation of amphipathic lactoside primers with consequent inhibition of endogenous glycosphingolipid synthesis.

The incubation of amphipathic lactosides with cultured cells was found to prime the glycosylation of lactosides whose oligosaccharide structures were exactly the same as those of glycosphingolipids produced by cells: B16 melanoma cells produced alpha2-3 sialylated lactosides; and PC12 cells, Galalpha1-4- and Galalpha1-3Galalpha1-4lactosides. Analysis of the cell-associated glycosylated products indicated that C16 series lactoside primers function 5-6 times more efficiently as acceptors than C12 series primers. The glycosylated lactosides were also secreted into the culture medium. Lactoside primers with longer hydrophobic chains hampered the release of glycosylated products from cells. The presence of an N-acyl chain in the lipophilic moiety of primers suppressed the secretion of glycosylated products. Owing to its overall availability, lactosides with the C12 alkyl chain were glycosylated 2-3 times more than C16 series lactosides and 1.4 times more than lactosides with the C12 acyl chain. C8-lactosides did not function as primers under the conditions of this study, but they were found to be the best acceptors for sialic acid transfer with the soluble enzyme fraction. The incubation of cells with 10 microM N-hexadecanoylaminoethyl-beta-O-lactoside caused a 30% decrease in endogenous GM3 of B16 cells and a 34% decrease in Gb3Cer synthesis of PC12 cells. The results of the present study demonstrate that lactoside primers serve as an efficient means to inhibit endogenous glycosphingolipids in studies to clarify glycosphingolipid functions.